Preformed strip and method for splicing conveyor belts

ABSTRACT

A preformed strip ( 20 ) of unvulcanized rubber having two-strand receiving grooves portions ( 22 A and  22 B) for splicing the ends ( 11, 12 ) of steel cord or strand reinforced rubber conveyor belts ( 10 ) is disclosed along with a method of forming the spliced joint.

TECHNICAL FIELD

This invention relates to a method and apparatus for forming splices atthe ends of conveyor belts.

BACKGROUND OF THE INVENTION

Conveyor belts are commonly used as a means to move material from onelocation to another. In large mining operations, the conveyor belt isgenerally formed of a rubber body embedded with steel cords or strands.A cover compound can be used at the surface wherein the material is tobe conveyed. Generally the compound is very abrasion and cut resistantand of sufficient thickness to prevent the rocks being conveyed fromtearing the belt. A pulley compound can be used on the interior surface,this rubber is ideally suited for improved wear as the belt traversesover the pulleys used to drive the belt.

These steel corded or stranded belts may extend several miles and costmillions of dollars to install and fabricate. The fabrication of suchbelts occurs initially at a factory wherein steel strands or cords arearranged in a coplanar relationship parallel to the surface of the beltso that the belt will exhibit uniform expansion and minimize weaving asit traverses which can cause belt damage.

The prior art method of fabricating belts requires the steps ofvulcanizing the rubber belt and winding it onto large spools forshipping to the site. Once the spools of belt are received at the site,the ends must be prepared for splicing by removing the vulcanized rubberfrom the strands over a distance determined to be sufficient to provideenough joint length to make a secure splice.

Removal of the rubber can be a very time consuming and tedious task.Often times piano wire is used to peel the vulcanized rubber from thestrands. In large belts of several feet in width over a hundred strandsmust be exposed at each joint end. Once exposed, the strands had to becleaned of as much of the vulcanized rubber as possible. The strandswere then cleaned with solvents such as toluene and then a bonding agentwas applied comprising a 3:2 mixed solution of “Chemlok No. 203” andxylene, for example, and rubber cement is applied to the strands anddried. After the preparation of both ends as described in U.S. Pat. No.3,487,871 entitled “A METHOD OF JOINING CONVEYOR BELTS HAVING STEELCORDS EMBEDDED THEREIN” granted Jan. 6, 1970, a joining member is formedmade of vulcanized or semi-vulcanized rubber of the same quality as therubber used in the formation of the belt. The upper face of the memberis preferably made of a non-vulcanized rubber and provided with aplurality of strand receiving grooves. Once the strands are in place, abonding agent of the type described above is preferably coated on thefaces of the surfaces to insure complete bonding. While this prior artpatent use the term “non-vulcanized rubber” being preferable at themelting surfaces of the otherwise vulcanized or semi-vulcanized member(13), it is believed that the term means “having at least its uppersurface formed of incompletely vulcanized rubber” as was required in theclaim of the patent. An important limitation when the member forsplicing is semi-vulcanized at this grooved surface, the use ofsemi-cured rubber forced the use of bonding solvents. These solvents arehigh in VOC's and the liberal use of xylene and toluene createscarcinogenic risks to the personnel. In developed parts of the world,the use of such solvents is greatly discouraged.

A second limitation of the prior art splicing member is that the memberwas apparently molded to the exact width of the belt and had exactlytwice the number of strands as the belt. This meant that for each beltwidth, there had to be a unique member since conveyor belts are notstandardized in width or in the size or in the number of strands to usethe concept taught in that patent required specially designed molds.

A third limitation of the method of splicing described in U.S. Pat. No.3,487,871 was that the strands had to be free of any of the vulcanizedbelt rubber which, if left on the strands, adversely affected thebonding.

The most relevant prior art document is considered EP-A-0 372 510(Stahgruber Grunber & Co. Otto) which has the feature identified in thepreamble of independent method claim 4.

An object of the present invention is to eliminate the need tosemi-vulcanize the splicing member.

Another objective is to make the use of solvents unnecessary.

Still another objective is to eliminate the need to completely strip thestrands of all vulcanized rubber prior to splicing.

A still further objective is to provide a splicing strip that can beused in multiples independent of the width of the belt or thecorresponding number of strands.

A still further objective is to improve the splice strength while savingtime in splice preparation.

SUMMARY OF THE INVENTION

A method of splicing the ends (11, 12) of conveyor belts (10) havingvulcanized rubber (2) with steel strands (1) embedded in the vulcanizedrubber is disclosed. The method has the steps of (a) removing a portionof the rubber (2) from the belt ends (11, 12) to be joined exposing aplurality of strands (1); (b) providing preformed unvulcanized strips(20) of rubber, in an array of bottom strips (20) each strip (20) havinga concave quarter-circular profile wherein strips (20) when laidadjacently to each other form stand receiving grooves (22) located on anupper surface (24), (c) placing exposed strands (1) of the belt ends(11, 12) being joined in the grooves (22) of the bottom strip (20); (d)placing top strips (20) overlying the array of bottom strips (20) andvulcanizing the strips (20) together thereby forming the spliced joint

In a preferred method, the step of removing the vulcanized rubber (2)exposing a plurality of strands (1) includes leaving the strands (1) atleast partially sheathed in the vulcanized rubber, most preferably in acoating of the vulcanized rubber (5) whereby the step of vulcanizing thestrips (20) together includes vulcanizing the strip (20) to the at leastpartially sheathed strands (1).

The step of providing at least two arrays of unvulcanized strips (20) ofrubber includes the steps of providing at least two bottom strips (20)and positioning the strips (20) adjacently to increase the width of thestrips (20), and cutting one of the at least two bottom strips (20)parallel to the grooves (22) thereby substantially matching the totalwidth of the adjacently layered strips (20) to the conveyor belt width(W_(B)).

The array of top strips (20) of similarly grooved as the array of bottomstrips (20). Preferably, the top and bottom strips are the same incross-sectional profile.

The step of providing the top or bottom strips (20) includes the stepsof extruding the strip (20), the extruder having a die (356) having apredetermined cross-section for forming the strips (20) forming thestrand receiving grooves (22) of the upper surface (24).

Each strip (20) has a predetermined cross-sectional profile having aflat base, a first side and a second side extending between the flatbase and an upper surface, the first side having a concave surfacehaving a quarter-circular shape or depression intersecting the topsurface and extending along the length of the strip (20).

In one alternative embodiment, the second side has a substantiallystraight profile. In the preferred embodiment, the second side has aconcave surface having a quarter-circular shape.

Each of the above methods of splicing uses an unvulcanized elastomericstrip (20) for splicing steel cable reinforced belts (10), the strips(20) having a base (W_(S)) and length (L_(S)). The strips (20) arecharacterized by an uncured strip (20) having a predeterminedcross-sectional profile having the base (W_(S)), an upper surface, afirst side and a second side, each side extending between the base andan upper surface. The profile having two substantially quarter-circulardepressions extending parallel along the length of the strip, eachdepression providing substantially half of a steel cable receivinggroove (22) for placement of a steel cable or strand (1).

It is preferred that strips (20) has a width of the base (W_(S))requiring a plurality of strips (20) for each splice joint.

Most preferably, the strips (20) are prepackaged in spools of continuouslengths of four or more strips (20) for each splice joint.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a fragmentary cross-sectional view of an exemplary beltstructure having steel strands embedded in vulcanized rubber.

FIG. 2 is a perspective view of a belt end prepared for attachment to acorresponding belt end and a plurality of the preformed unvulcanizedstrips (20) of rubber for joint splicing.

FIG. 3 is a steel cord strand shown sheathed in a coating of thevulcanized belt rubber.

FIG. 4 is a side elevation view of a vulcanizing press for forming abelt joint in accordance to the invention.

FIG. 5 is a perspective view of a extruder apparatus for forming thepreformed elastomeric strip.

FIG. 6 is a cross-sectional view of the extruder die with a profile forforming the strand receiving grooves in the strip.

FIG. 7A is a cross-sectional view of a preferred strip (20).

FIG. 7B is a cross-sectional view of an alternative strip (200).

FIG. 8 is a cross-sectional view of a preformed strip with a layer ofbottom pulley rubber laminated to the strip.

FIG. 9 is a cross-sectional view of a preformed strip with a layer oftop cover rubber laminated to it.

FIG. 10 is a perspective view of the strip on a spool for splicing ajoint for a belt reinforced with steel strands embedded in rubber.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, an exemplary conveyor belt (10) will beobserved. The belt (10) has a plurality of steel cords or strands (1)embedded in a core or central layer of rubber (2). As illustrated, thecentral layer (2) is bounded by a bottom layer of rubber (3) of acompound ideally suited for contacting the drive pulleys of the conveyorsystem (not shown) and a cover layer (4) of a rubber compound ideallysuited for abrasion and cut resistance. Additionally, such belts (10)may include additional textile or fabric layers or alternatively areformed utilizing only a single homogeneous rubber without a top orbottom compound while the steel strands of the belt may be impregnatedor coated with a thin rubber bonding layer or sheath (5) to enhance cordadhesion. Nevertheless, the present invention is ideally suite tofacilitate the splicing of almost any known type of rubber conveyorbelts (10) having steel cords or strands (1).

As shown, preparation of the belt ends (11, 12) to be joined isillustrated in FIG. 2. The belt ends (11, 12) has a portion of the body(14) of the belt (10) removed to expose the steel strands (1). Forconvenience, the term “body (14) of the belt (10)” is intended toinclude all body elements such as the central layer (2), the bottom (3),the cover (4), and any other layers. That portion of the body (14) isremoved preferably across the width of the belt in a diagonallyextending direction. This insures that the splice seam will not approacha drive pulley simultaneously. Additionally the layer of rubber on thetop surface of the strands may be cut back further than the lower layerof rubber below the stands, this method of ends (11, 12) preparation iscommonly referred to as a sped contour. These features, although notrequired, can improve the splice joint in some applications.

Once the rubber body (14) is removed from an end (11, 12), the stands(1) of steel cord are exposed. In some techniques of removing the rubberbody (14) steel piano wire is used to peel the rubber off the cords (1).In that method of body removal (14), virtually all of the rubbersheathing the steel cord is removed such that the cords are only atleast partially sheathed in cured rubber. If desired, the remainingrubber bonded to the cords or strands can be removed by wire brushes orthe like. This technique is quite tedious and time-consuming, however,and is preferably avoided.

An alternative method of removing the rubber body (14) includes using ameans having contoured cutting surfaces that remove the rubber body (14)while leaving the strands (1) coated in a thin sheath of rubber (5) asshown in FIG. 3. In this technique, the strands (1) can be buffed toenhance the adhesion of the cured rubber sheath (5) prior to splicingthe joint.

It is important to note that the present invention is ideally suited tobe used on belts; wherein the strands are exposed at the end of thebelts as a result of a technique of manufacture. In such a case, thestep of preparing the ends (11, 12) for splicing can be avoided ormodified eliminating the step of removing the cured rubber.

As shown in FIG. 2, the exposed strands or cords (1) are ideally placedin depressions (22 a, 22 b) in preformed strips (20) of unvulcanizedrubber. These depressions (22 a, 22 b) each represent a portion of astrand receiving groove (22). Ideally, the number of grooves (22) perinch are twice the number of strands per inch at one end of the belt.

Each preformed strip (20) of rubber splicing has a base having a width(w_(S)) and a cut to length L_(S) as shown in FIG. 2. The strips (20)has a top surface (24) intersected by a plural of grooves portions (22a, 22 b) each groove portion being a portion of either a first side (25)or a second side (26) of the strip.

By orienting the strips (20) into an array of bottom strips (20) withthe grooved portions 22 a and 22 b of adjacent strips (20) form grooves(22) adjacent the strands (1), the stands (1) of one end (11) can beplaced in every other groove (22) while the strands (1) of the other end(12) fills the grooves (22) remaining to be filled. The resultingstrands (1) from end (11) and those from end (12) form an overlappingarray of strands (1).

Since the number of stands (1) in the splice joints are approximatelydouble the number of strands in the rest of the conveyor belt (10), itis possible to vary the length of the cords or strands (1) in a numberof patterned sequences. The principle concept being that a cord (1) cutshort in end (11) would be adjacent one or two long cords (1) in end(12) and vice-versa The resultant effect is that the cords' ends do notbend around the drive pulley at a simultaneous occurrence giving rise toa peak stress. While these splicing techniques are well known in theart, it is important to note that they are easily adaptable to thepresent invention.

Once the cords or strands (1) are all placed in the grooves (22) in aproper splicing sequence, an array of top strips (20) is placed over thesplice opening covering the strands with an array of uncured rubberstrips (20) on both the top and bottom.

Preferably, the top strips (20) may be grooved similar to the bottomstrips (20). Most preferably, the top and bottom strips are the same inprofile and composition.

Alternatively, the top may simply be a flat sheet of uncured rubber.

Dependent on the amount of opening needed for the splice joint, thestrip (20) may be provided in a large spool of continuous length, insuch a case, the strips may be trimmed to fit as needed.

Alternatively, the strips can be sized in terms of length to provide theoptimal splicing length L_(S) for strength and durability and noadditional trimming or cutting of the strips (20) would be recommended.In this case, the belt manufacture can at least insure the splice lengthis sufficient.

In terms of strip width (W_(S)), an important feature of the splicingstrip is that they are preformed to a base width (W_(S)) that isgenerally about equal to the cord (1) spacing as measured at cordcenters. In bets having a width of five feet or more, it can easily beappreciated that the many strips are easier to handle if nested in aplaten or fixture. The splicing operator simply can place as many stripsas are needed to cover the strands and then must trim cut the last stripto substantially match the overall belt width. Ideally, this trimmingsimply requires taking a hot knife or similar cutting element andpassing it through a groove portion (22 a or 22 b) of the strip (20).This procedure is applicable to both the top and the bottom of thesplice joint.

Once the unwed strips (20) are positioned and the strands properlyplaced in the grooves (22), the joint area is placed in a curing press(30) as is shown in FIG. 4. Once cured, the splice is complete. Theadvantages of precision and quality control improvements can be easilyappreciated over the more arcane techniques used in the prior art but,in addition to making a superior splice, this method can reduce splicingtime by as much as half over current techniques. When one considers thatas many as a hundred splices may be needed in a large mining belt, areduction from 8 hours to less than 4 hours to complete a single splicejoint has obvious cost and time savings.

In FIG. 5, an extruder (100) is shown for forming the preformedelastomeric strip (20). The extruder (100) has a die head (356) thatshapes the strip's profile. A conveyor mechanism (120) can be used toorient and cool the formed strip.

In FIG. 6, the die head is shown profiled to form depressions or grooveportions (22 a and 22 b) in the cross-sectional profile of the strips(20), these groove portions (22 a and 22 b) form the strand receivinggrooves (22). One extruder with preferably only one die head (356)having the groove forming portions (22 a and 22 b) can establish theoverall profile of the strip (20) in a variety of sizes by simplyvarying he extrusion speed and tension. The strip (20) itself is formedby forming, cooling and delivering the uncured rubber to a spool (40).As the strip profile is formed, the strip (20) is transferred directlyonto a conveying means (600) to allow the strip to cool.

Alternatively, the strip (20) can be transferred onto another layer ofrubber (3, 4). As shown in FIGS. 8 and 9 respectively, the preformedstrips can be laminated onto a layer of bottom pulley rubber (3) or ontoa layer of top cover rubber (4), thus, making specific top strips (20)and bottom strips (20). In such a case, a duplex extruder can be used tosimultaneously form the two layers as shown in FIG. 5.

It is believed preferable to transfer the strip (20) onto a carriermember such as liner (50). Most preferably a poly liner (50).

As shown in FIG. 10, the strip (20) when placed on a liner (50) can becoiled and spooled. Assuming the strip (20) is attached or transferredonto the liner (50) at the location where it is formed, i.e. at theextruder, then the adhesion to the liner (50) is such that the strip(20) will be securely fixed to the liner (50). This minimized thepotential for shipping and handling damage. As shown, the length ofstrip (20) on a spool should be equal to the amount needed to make asplice joint.

Nevertheless, the principles of forming strips (20) advantageouslyenables the component to be preformed in a green or uncured state. Thisinsures that the strips (20) can be used without the necessity of usingsolvents and cements.

What is claimed is:
 1. The method of splicing the ends (11, 12) ofconveyor belts (10) having vulcanized rubber (12) with steel strands (1)embedded in the vulcanized rubber comprising the steps of: exposing aplurality of strands (1); providing two arrays of unvulcanized strips(20) each strip (20) of rubber having a preformed cross-sectionalprofiles, one array of strips (20) being an array of bottom stripshaving a plurality of substantially parallel strand receiving grooves(22) the other array of strips (20) being an array of top strips;placing the exposed strands (1) of the belt ends (11, 12) being joinedin the grooves (22) of the one array of bottoms strip (20); placing thearray of top strips (20) overlying the array of bottom strips (20) andvulcanizing the strips (20) together and to strands (1) thereby formingthe spliced joint, characterized in that: the steps of exposing aplurality of strands includes removing a portion of the belt ends to bejoined, providing a plurality of bottom strips, each bottom strip havinga preformed cross-section of profile having a base width (W_(S)), thebase width (W_(S)) being about equal to the cord spacing as measured atcord centers, and two quarter-circular groove portions (22 a, 22 b) andpositioning the plurality of bottom strips adjacently to increase thetotal width of the plurality of bottom strips and form grooves (22), andcutting one of the bottom strips parallel to the grooves, thereby,substantially matching the total width of the plurality of strips to theconveyor belt width (W_(B)).
 2. The method of splicing the ends (11, 12)of a conveyor belt (10) of claim 1 wherein the top strips (20) havegrooves (22) similar to the bottom strips (20).
 3. The method ofsplicing the ends (11, 12) of a conveyor belt (10) of claim 1 whereinthe top and bottom strips (20) are the same.
 4. The method of splicingthe ends (11, 12) of a conveyor belt (10) of claim 1 wherein the step ofproviding the top or bottom strips (20) includes a step of extrudingstrips (20), to a predetermine profile, the profile having groovepotions (22 a and 22 b).
 5. The method of splicing the ends (11, 12) aconveyor belt (10) of claim 1 wherein the step of extruding includes thestep of simultaneously forming the bottom strip (20) and a strip ofpulley contacting rubber compounds at the extruder, thereby forming adual compound bottom strip (20).
 6. The method of splicing the ends (11,12) a conveyor belt (10) of claim 1 wherein the step of extrudingincludes the step of simultaneously forming the top strip (20) and astrip of top cover rubber compound (4), thereby forming a dual compoundtop strip (20).